1. Field of the Invention
The present invention relates to a panel assembly and a panel forming apparatus, and more particularly, relates to a panel assembly having a stringer and a sheet panel clampingly secured to projections and recesses provided on the stringer and an apparatus for forming said sheet panel.
2. Description of the Prior Art
A panel assembly is disclosed in the Japanese Patent Publication Nos. 42-26591, 46-14394 and 44-11699, for example.
The conventional panel assembly comprises a stringer 1 and a plurality of panel elements 2, as shown in FIG. 1.
The stringer 1 is formed of a plate-of aluminum alloy, for example, by press working in a predetermined figure shown in FIG. 1 and bent so as to have a U-shaped cross-section as shown in FIG. 2. The stringer 1 can be formed by molding a plastic material instead of the aluminum alloy. The stringer 1 has projections 5a each having convex portions 3 at both sides thereof and recesses 5b each having concave portions 4 at both sides thereof. Each of said projections 5a and each of said recesses 5b are arranged alternately with a constant interval on the top of each of side walls of the stringer 1.
Each of said panel elements 2 is formed of a baking finished plate of aluminum alloy or plastic and has convex portions 6 at both sides thereof.
A first panel element 2 facing upward is clampingly secured to the recess 5b formed between the projections 5a of the stringer 1 and a second panel element 2 facing downward is put on the projection 5a of the stringer 1, so that the two curved edges 6 of the second panel element 2 are hooked around the two curved edges 6 of the first and third panel elements 2 clamped in the recess 5b to form a panel assembly.
The conventional panel assembly can be fabricated in the following manner.
One of the two curved edges 6 of the second panel element 2 to be clamped on the first projection 5a is hooked, as shown in FIG. 1, around one of the two bent edges.6 of the first panel element 2 clamped in the first recess 5b adjacent to said first projection 5a. Thereupon the other of the two curved edges 6 of the second panel element 2 is hooked around one of the two curved edges 6 of the third panel element 2 which has to be clamped in the second recess 5b adjacent to said first projection 5a before the third panel element 2 is placed in the second recess 5b. The other curved edge of the third panel element 2 is then brought into engagement with the second recess 5b. There after, the second and third panel elements 2 are pressed into place.
As stated above, in the conventional panel assembly, it is necessary to arrange the panel elements 2 facing upward and facing downward alternately and to engage with the projections and recesses of the stringer 1, respectively, and accordingly the work becomes hard and the panel assembly becomes expensive. Further, the conventional panel element is limited in width, so that it is difficult to form a panel assembly of large area. If the number of panel elements of the panel assembly is increased, some of the panel elements are not mounted precisely on the stringer, so that there is a danger of leaking of rain in case that the panel assembly is used as a roof, for example.
As a result of the studies and experiments it was found that a sheet panel of aluminum alloy or plastic consisting of a plurality of panel elements 2 could be obtained by a press working and that each of the panel elements 2 could be clamped on each of the projections and recesses of the stringer, respectively, by the resiliency of the sheet panel.